People Killing People
by d0lli
Summary: New York city is changing. And all Mac Taylor can do in the face of it is keep on fighting. Short Prototype/CSI:NY crossover.
1. Chapter 1

**Title: **People Killing People.

**Rating: **Very mild gore and violence.

**Summary: **New York city is changing. And all Mac Taylor can do in the face of it is keep on fighting.

**Disclaimer: **It all belongs to not me. I stole the title too.

**A/N: **Recently completed Prototype on the PS3 and couldn't stop imaging possible CSI scenarios while decimating the city. Thus, a little encounter was born. You don't have to have played Prototype to get it but it helps and you should anyway cause it's awesome. I might add to this if the notion strikes me, but right now it's a oneshot. I apologise for my apparant dislike of more than two sentence paragraphs and the ever present abuse of the comma. Critique very much appreciated.

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It was common knowledge to anyone who knew him that before joining the New York crime lab, Mac Taylor had been in the Marines.

It was a sign of his strength that he had seen so much of the horrors that people could inflict upon one another and yet he still continued to fight against it. He knew how to fight and he was good at it. But he'd never seen anything like what they were dealing with now.

Just over two weeks ago, things had started to change in the city of New York. A sudden mysterious and aggressive military presence could hardly go unnoticed, but that had only been the beginning.

It had been the corpses that warned them something truly terrible was going on.

Mac had realised in the moments standing over the mutilated body of a middle aged woman that he had rarely seen Sid genuinely frightened. Angry, confused, saddened maybe… but as he explained that the teeth that had torn the woman's flesh from her bones had been human, Mac had recognised that fear with a chill of premonition.

Everything since then seemed to him to have followed in an almost incomprehensible blur of shock, of running, of blood and screams and the smell of infection.

It was a smell they'd come to know well. A smell they'd come to associate with terror.

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'Mac, we need to get out of here!'

Stella's shout was almost drowned out by the hoarse screams of the hoard of infected stumbling toward them. Mac grit his teeth, his gaze flickering desperately between the blank walls of the alley and the growling, shuddering mass of bodies.

They were trapped. His grip on his gun intensified and he opened his mouth to tell the rest of them to get back while he tried to thin their numbers, when something unexpected happened.

A good portion of the infected seemed to explode in a shower of blood and body parts and the rest turned their attention to some threat that had appeared behind them, at the entrance to the alleyway. Something that looked organic and alien cut through them, swinging through the air like a deadly whip, crunching into the ground and smashing bodies against the walls with incredible force.

Within seconds the crowd of zombies had been decimated, leaving the exit clear.

Mac held still, his gun pointed steadily at the street, Stella, Danny and Don frozen in the same stance behind him, hating the weight in his gut that told him some new monster had come to hunt them. His blood thrummed through his veins like thunder, his heart shuddered in his chest with the effort of keeping his breathing steady and his sight held firm.

He heard Danny suck in a breath through clenched teeth at the sound of the first footstep and felt the next echoed in the twitch of Stella's body behind him. The figure didn't so much emerge from the shadows as seem to coalesce from amongst them and after a second of staring intently, Mac realised it was a man.

He didn't relax his stance. The city had taught him not to trust his eyes.

The man was tall and imposing in a black leather jacket with a grey hood pulled over his head, but it wasn't his clothing that made Mac wary. There was something in the way he stood with his head slightly bowed and his shoulders strangely stiff, arms hanging loose at his sides – it was a ready, sturdy bearing but it was unafraid. His head tilted slightly as he moved, as though he were constantly listening, constantly aware.

This man had nothing to fear here.

In a flicker of movement that was both sudden and slow, Mac found himself meeting cold blue eyes staring out from a shadowed face that had all the appearance of humanity and yet lacked any semblance of it at all. He took a deliberate step toward them and panic coiled in Mac's gut with alarming intensity at the instinctive realisation that they were facing the most deadly predator on the streets of New York.

He didn't realise he had taken an automatic step back until the echo of his companions footsteps told him they'd done the same. For a second he swore he saw a cold smirk slide over the man's face before his head jerked to the side as though reacting to a sudden noise. Sure enough, a mere second later, a terrible roar echoed along the buildings and shuddered down Mac's spine – he recognised it as the call of one of those mutants that came from the hives.

The man responded strongly to the sound, burning rage flickering over his face and his muscles tensing in a display of emotion that took Mac by surprise. The coldness he'd perceived in this creature before them was washed away as something smouldering and powerful took its place.

He paused to turn his gaze on them again, considering, and Mac thought of mist and black ice and nightmares, and almost prayed.

Then his head tilted downward once more and in a flash of movement he was gone.

Without thinking, Mac moved quickly out into the street, the others following and they watched as the figure of the man sprinted down the street, vaulting the wrecks of cabs and piles of bodies with ridiculous ease. His movements were smooth and sure and when he flipped over a heap of rubble and continued to sprint along the side of a building, swerving and spinning over ledges and fire escapes, it seemed completely natural.

They watched until he was out of sight and then there was silence.

Mac let his breath out in a rush and closed his eyes against the reality he found himself in, the constant wash of shock and fear pulsing heavily behind his eyelids. He furrowed his brow against the sensation and only opened them when a snort and a muffled curse pulled his gaze to Don.

The bags under his eyes and smears of blood and dirt across his face somehow couldn't totally diminish the familiar sardonic tilt to the Detectives eyes as he rolled his shoulders and huffed.

'I dunno why I bother being surprised anymore.'

Then he checked his gun and turned to walk back toward the safe house.

The rest of them shared a rare smile and followed.

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	2. Chapter 2

**A/N: **This came about much quicker than I expected. Guess I never thought there'd be any interest, so thanks to everyone who reviewed the first chapter, you obviously inspired me. Hope this delivers! And many thanks as always to my lovely electric_dreamer for all the encouragement.

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They'd been crouched on top of the building for half an hour now. Tired and out of ideas, they could do nothing but watch as crowds of shuffling infected screeched and pounded at the walls of the safe house across the street.

It was maddening to be so close and yet so powerless.

When Mac had returned with Stella and Hawkes from another fruitless search for their missing friends only to find a swarm of growling monsters blocking their path, he had experienced a surge of hopelessness that almost brought him to his knees. It had passed in seconds, but he could feel it sitting cold and hard in his chest, waiting for him to let his guard down so it could overwhelm him.

He was finding that anger was as good a way as any to keep it under control.

'We can't stay here forever. We have to do something.'

Stella sighed in response to his furious mutter, the sound bone-weary but still not lacking her usual spark.

'You're right Mac, but we need a plan. And so far we don't have one. So we need to wait.'

It was the same thing she'd been saying to him since they'd scrambled to their current vantage point, in one way or another, and he appreciated her voice of reason when he was feeling so frayed. Stella was one of few people who could recognise when he needed a steadying hand and maybe the only one who was never afraid to give it to him. But his frustration was eating him up as he imagined Don and Danny crouched on the second floor of the building, trying to keep the few civilians they'd managed to find calm, not knowing if the rest of them were safe, listening to the pounding of the dead against the walls.

Mac didn't like letting his friends down. He didn't like feeling like a coward. He opened his mouth to growl a response to Stella, knowing she'd rise to the bait, beat him down, make him see sense - before being cut short by Hawkes' soft voice.

'I know its tough Mac, but Stella's right. Getting ourselves killed won't do the others any good.'

The steady calm the doctor exuded seemed to sink into Mac's skin and dampen the fire of frustration and he exhaled in slow annoyance. Gratitude for his companions washed over him and he let his shoulders relax a little.

'I know. But we _can't_ wait forever. Maybe we should just make a run for it and see how many we can take out…'

'You'd never make it.'

The three of them spun around at the new voice behind them, guns aimed and steady - then both Mac and Stella twitched in recognition at the sight of the man before them.

He was tall, wearing a black leather jacket with a grey hood pulled over his head, and his blue eyes burned like ice.

Fear traced a familiar path down Mac's back and his knuckles whitened.

'You.' He was surprised when his voice didn't shake. 'Who are you? What do you want?'

It had been a few days since their strange encounter in the alleyway but Mac's nightmares had given him ample time to consider the mystery of this stranger and the terror he inspired. It didn't surprise him that the man was no less chilling in the daylight – if anything it made the shadows on his face more pronounced and his eyes glowed amongst them.

Right now those eyes were fixed on him with unpleasant intensity.

'You're Mac Taylor.'

The voice was rough and deep, like he wasn't accustomed to using it or it had been hardened by screams and roars, and he spoke with a certainty that almost made Mac shudder. He resisted the urge to swallow and kept his voice strong and commanding.

'That's me. Now answer my questions.'

That same sliding tilt that was almost a smirk passed over the man's mouth before he spoke again.

'My name is Alex Mercer. And I need your help.'

The absurdity of this statement left them all momentarily speechless.

Mac searched in vain for something he could recognise in that face, something he could identify, some clue as to what was really going on here. But there was nothing. It was like looking into a void. So he kept his gun pointed between Alex Mercer's eyes and tried the direct approach.

'My help with what?'

Mercer swayed from one foot to the other, a strange motion, almost like a boxer keeping himself on the balls of his feet while he waited for the bell to sound. He pulled his gaze away and swept it along the city around them, gesturing slightly with his arm, his shoulders rolling like he was bracing himself – every slight movement was odd, laced with hostility, constantly prepped for attack.

'You want to put an end to this. Right?'

Mac narrowed his eyes, tried to find the hidden motive.

'Right.'

'You want to find the people responsible. Right?'

'…Right.'

The blue gaze snapped back to him and Mercer spread his hands apart with palms up, a passive motion that somehow had a hint of mocking to it, like he was imitating a gesture he found amusing in someone else.

'That's what I want too. Whoever caused all this… they changed me. They took everything from me. And I'm gonna make them pay.'

The already deep voice dropped a further octave on the last few words, turning them to the growl of something purely predatory, and the first hint of emotion Mac had yet seen pulled Mercer's lips from his teeth in a snarl.

If there hadn't been a wall behind him, Mac knew he would have stepped back in the face of such fierce rage and determination. The words held the echo of a mantra, of promise and prayer, of the kind of words a man muttered to himself when there was nothing more to live for… There was no question of whether or not he would do this thing - only a matter of when.

Mac took a deep breath in through his nose and let it out before he spoke again.

'So why me?'

The predatory gleam receded and the mocking casualness was present again in the shrug of leather covered shoulders.

'You come highly recommended. Dr Bradley Ragland sent me to find you.'

'Ragland?' It was Hawkes who spoke, the jolt of familiarity clear in his tone, 'I know Ragland - used to work with him.'

The words were directed at Mac, though he kept his eyes on Mercer and his jaw tightened when that gaze switched to him.

'You're Sheldon Hawkes?'

If the fact that he knew his name had any affect on Hawkes, he didn't show it, just nodded stiffly, his mouth a thin, tense line. Mercer hummed in acknowledgement.

'Well he told me you were Detectives. He said if anyone would be able to get to the bottom of all this, it would be you. So I'll make a deal with you.'

The revulsion that swept through Mac at the thought of continuous contact with Mercer was surprising and almost physical – he struggled not to flinch, to swallow the bile at the back of his throat. It was as though some primal and fundamentally human part of him recognised on instinct that there was something alien in Mercer that was to be feared and destroyed.

But Mac wasn't in the habit of letting his instincts overcome him. He knew they needed help. So he beat down the pulse of that primitive part of himself and met the blue gaze unflinchingly.

'What kind of deal?'

Mercer's smile was like a shark's – nothing but teeth, even if you couldn't see them all.

'Your missing some friends aren't you? I can help you find them. And I can protect you long enough to get them somewhere safe.'

Outwardly, Mac's only response was a frown, but his mind was suddenly whirring. Mercer's help would be undeniably valuable – they'd seen him destroy a crowd of over fifty infected without breaking a sweat, and tear down a street faster than any moving vehicle Mac had ever seen. They could find the others, Lindsay and Sid and Adam, and they might even live to get out of this hell.

It was Stella who voiced his only concern.

'And in return, what..? We help you get revenge?'

Mac could tell she was trying to keep her voice neutral, but the scorn she placed on the word 'revenge' was obvious. Mercer looked at her and Mac fought the urge to step between them, shield her somehow – it was unneeded anyway. She met the gaze dead on, with the familiar spark of challenge.

'Yes.'

She slid her eyes to meet Mac's and he could practically see her following his thought process. She knew as well as he did that it didn't matter how much they disliked the idea… if Mercer was their best chance of finding their friends alive, they had to take it. Her eyes conveyed her understanding and she nodded almost imperceptibly. Mac turned to Hawkes who flicked his dark gaze to his for a brief second and jerked his head in agreement, his own decision already made.

'Ragland's a good man,' he muttered, explaining, 'he wouldn't have sent him if he thought he'd hurt us.'

Mac took a deep breath and looked at Mercer. The man was watching them all with something like wariness in his gaze, but it was armour plated. Mac briefly wondered what he would do if they said no… or if they failed… He pushed the thought quickly away and lowered his gun, aware of Hawkes and Stella doing the same.

Two very different men regarded one another steadily, both feeling their own kind of anxiety, both trying to fathom out what the other was thinking... while the screeching cries of the damned drifted around them.

Mac sighed, 'Don't make me regret this.'

For just a second, he thought Mercer seemed… relieved. Then the glimmer of emotion passed and he was rolling on his feet, moving to stand on the other side of Stella, his steps slow and almost lazy – but as with every other move he made, the potential for sudden violence was ever present.

'You have people in there?'

Mac suspected he knew the answer to that already, had probably been watching their desperation long before he confronted them, but Stella answered him anyway with her usual brisk efficiency.

'Two of our guys and about five armed civilians – they're brave enough but they're jumpy, untrained. There's a garage that opens onto the street and we've got a pretty heavily armoured truck that'll carry us all,' she pointed to the grill that hid the underground parking lot as she spoke, 'but with this many infected, we'd be swamped before we got five feet. Danny and Flack are on the second floor - we'd need to get in, let them know what's going on and get everybody downstairs before making a run with the truck.'

Mercer absorbed this information while his eyes flickered quickly over the windows of the second floor, the entrance to the garage, the infected staggering around the building and clawing at the doors. He nodded steadily.

'You need time. I can give you that. Get in, get everybody in the truck and get them out. Then head for the nearest military blockade.'

He leapt smoothly up onto the ledge and continued to talk with his gaze fixed on the street below.

'I'll take care of them. Start making your way down and when I say so, run for the building.'

Stella glanced at the street swarming with lumbering infected and muttered stiffly,

'But there's so many of them.'

'Don't worry,' Mercer replied easily, before flicking his arms out to his sides and as he did so, giant claws seemed to emerge from his flesh. Stella flinched and stepped back, the three of them eyeing the blackened, wicked looking spikes without breathing.

He spared them a glance, and there was bitter satisfaction in his gaze.

'I'm a one man army.'

Then he jumped off the ledge.

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End file.
